1) Full backup
All the file are put into media during full backup.
The advantages are:
- Restoring from a full backup lowers the tape handling activities compared to an incremental or differential backup.
- The content from media is from within the same backup window (rollback and redundancy)
The disadvantages are
- The backup window is wide.
- if the data does not change, every full backup media contain the same data.
2) Differential backup
The diffrential backup strategy first look for the modification time of file and comparre it with the last full backup time. Differential backup are clumative; once a file has been modified, it may be included in every differential backup untill the next full backup.
The advantages are
- To restore, the latest full backup and only the latest differential backup media sets are needed.
- The backup window is smaller than a full backup.
The disadvantages are
- If data changes a lot between full backups, the data to back up tends to grow a bit over time, using more media.
Incremental backups are similar to differential backups in that both back up only modified files.
Incremental backup checks the difference between the modification time of a file and the last backup time (either being full or incremental backup). If the modification date is more recent than the last backup date, the file is backed up.
The advantages are
- The backup window is smaller than a full backup.
- Only the differences from a previous backup will be written on media.
The disadvantages are
- To restore, the latest full backup and all the subsequent incremental backup
media sets following that full backup are needed. - To restore a single file, tape handling operations are intensive.
- A damaged or lost media in the incremental set can mean disaster: The
modifications of those files on that media may be lost forever.
